Airfoils such as an aircraft wing assembly or like primary lift surfaces are customarily provided with secondary airflow modification members moveable with respect thereto in order to tailor lift forces. The most common arrangement as respects the preferred implementation of the present invention is the incorporation of flaps and slats on an aircraft wing moveable with respect thereto in order to control lift forces during landing, takeoff and certain other flight maneuvers. Historically flap and slat positioning has been achieved by various hydro-mechanical linkages. Customarily, the cockpit area is provided with a so-called flap handle which may be manipulated by the pilot between or among several desirable, pre-selected positions corresponding to correlative aerodynamic configurations for these high lift surfaces. The handle and/or its receiving structure typically bears legends or symbols indicative of the range of wing conformations facilitating pilot placement during the course of flight to achieve the desired or necessary airfoil contour. Cables are included intermediate the flap handle and e.g., hydraulic systems for translating movement of the handle into a suitable control signal. In turn, that signal is utilized to impel operation of rotary or linear actuators in communication with the respective flaps and/or slats. The hydro-mechanical linkages downstream of the cable assembly are considered to be reliable positioning devices of very close tolerance respecting the ability to position the associated surface. However, the cable segment of the overall system can be subject to positioning error as a consequence of, e.g., stretch on the input side of the assembly.
The present invention accommodates small, anticipated errors due to mechanical deviations and cable stretch on the input side of the system but isolates the same on the output side in order to achieve enhanced position accuracy. Dual, control-slaved cam assemblies are incorporated to achieve this desirable result. In that regard, the prior art acknowledges various control systems reliant upon plural cam units to achieve desirable control over the positioning of aircraft components.
U.S. Pat. No. 4,071,208 discloses a mechanical mixer for controlling aircraft spoilers and insuring proper positioning of same with various aerodynamic factors borne in mind. That mixer apparatus employs a three-dimensional cam mechanism formed with cam surfaces contoured to position aerodynamic control surfaces, such as spoilers, on the port and starboard wings in response to any combination of first and second pilot-controlled inputs, such as speed-brake and roll inputs respectively. First and second three-dimensional cam surfaces are defined on the cam which is itself moveably mounted on a support for translation along and rotation about a predetermined axis. Cam followers associated with the cams are likewise moveably mounted on the support in a manner permitting separate camming by the two cam surfaces. Port and starboard control surfaces are coupled to the first and second followers, respectively, and are displaced to predetermined positions of deployment in reaction to movement of the followers as determined by the first and second cam surfaces. The cam is translated in response to the first input to vary the profiles of the cam surfaces with which the followers mate when the cam is rotated by the second input. The cam surfaces are contoured such that variation in the profiles cause the positioning of the aerodynamic control surfaces in response to the second pilot-controlled input to be varied in a predetermined manner in response to the first pilot-controlled input.
U.S. Pat. No. 4,244,541 discloses another system where dual cam control is employed for coordinated deployment and retraction of leading and trailing edge wing flaps of an aircraft in response to a single pilot-operated control lever. That patent discloses a system which includes a primary cam member directly responsive to movement of the control lever and a secondary cam member slaved to the actual movement of the trailing edge flaps. The primary cam has dual cam surfaces, including a leading edge cam surface which acts through a leading edge follower to control the leading edge flaps and a correlative arrangement for the trailing edge flaps. The leading and trailing edge follower members in turn operate separate hydraulic subsystems to deploy (i.e., extend or retract) the respective sets of flaps in accordance with pilot-commanded movement of the primary cam. An initial partial displacement of the pilot-operated control lever causes the primary cam and associated follower to effect full deployment of the leading edge flaps, without deploying the trailing edge flaps. Further advancement of the control lever beyond a predetermined point causes the primary cam together with its associated follower to deploy the trailing edge flaps in addition to the previously deployed leading edge flaps. The secondary cam has a cam surface patterned after the trailing edge cam surface of the primary cam means; and as the secondary cam moves in concert with the actual deployment of the trailing edge flaps, a feedback follower cooperates with the trailing edge cam surface on the secondary cam to provide a feedback that is mechanically combined with the response of the trailing edge follower to the primary cam, to control a hydraulic subsystem that moves the trailing edge flaps to the commanded position. The disclosure continues with a specific improvement comprising an override follower cooperating with another cam surface provided on the secondary cam, which is patterned after the leading edge cam surface on the primary cam. Direct control over the deployment of the flaps is overridden when the actual position of the trailing edge flaps dictates a different position of the leading edge flaps than that commanded by the primary cam. Thus, the system accounts for and precludes the possibility of an undesirable flap configuration which might result from inadvertent, premature retraction of the leading edge flaps while the trailing edge flaps remain extended.
As can be seen from the general discussion of certain prior art devices as aforesaid, aircraft lift surfaces, including specifically aircraft wing flaps, have been controlled in the past by cam programming, including certain types of interactive cams for positioning members on the one hand and sensing position on the other. However, apart from such implementation in a conceptual sense, the utilization of cam programming in order to allow a single input (e.g., via the flap handle) to control mechanically the slats and flaps to position their respective high lift surfaces in accordance with separate programs required by aerodynamics of the craft, and monitor that position to yield a nulling control signal, has yet to be realized.